I'm looking for a sales forecasting model or formula specific to
retail companies.  I would like to forecast a retailer's overall sales
in 2005, 2006, 2007, 2008 based on sales, store, or relevant financial
data for 2000, 2001, 2002, 2003, and 2004.  My current model takes
each year's sales and store base into account and assumes that new
stores take a certain number of years to ramp up or down.

If you do find such a formula, I would appreciate as much explanation
as is available, as well as any information on the model's
reliability.

Please do not hesitate to ask for clarification.